this post was submitted on 29 Jun 2025
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Moire/Vernier Radius Gauge (www.printables.com)
submitted 2 days ago* (last edited 1 day ago) by monotremata@lemmy.ca to c/3dprinting@lemmy.world
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I previously posted this on Reddit, since it reaches more people there (and I didn't want to post everywhere at once, as it makes it harder to keep up with the comments). Sorry about that.

This is a tool for measuring the radius of a circle or fillet from the outside; it uses a moire pattern of slots and lines to enable a direct reading of the values from a vernier scale.

A video of a broken-open version makes it a little easier to see how the moire and vernier features operate: https://i.imgur.com/Ku2nBkq.mp4

More photos of a slightly earlier version are here, including the tool being used for actual readings: https://imgur.com/gallery/moire-vernier-radius-gauge-design-3d-printing-ajy0GBg

I was inspired by this post: https://makerworld.com/en/models/1505553-adjustable-chamfer-gauge#profileId-1575605

which is a gauge which measures chamfers using a sliding probe. The same user had also posted a radius gauge, which worked similarly, but it was much larger, using gears and two racks in it to amplify the motion, which I didn't initially understand. I asked about it, and he pointed out that, because of the geometry of the probing, the slider only moves a small proportion of the length of the actual radius being measured--about (sqrt(2)-1), or 0.414mm per mm of radius. Since we're drawing the marks with a 0.4mm nozzle, it's not really possible to make marks that close together and still have them readable.

So I thought, I bet you could fix that with a vernier scale. And then I had several thoughts all at once--that a lot of people are kind of scared off by vernier scales, and also that I bet you could fix that with 3d printing using the relationship between moire patterns and vernier scales. I don't think I've seen this done before, but it probably wasn't really practical before 3d printing. Arguably it's not entirely practical now, as the deep slots and parallax effects can make it a little hard to actually see the markings. But it was a fun experiment, and I think the result is eye-catching enough that it's probably got some educational value in getting people to actually think about how it is that vernier scales work. (It might even have educational value for things like number theory...e.g., it's important that the vernier factor involve relatively prime numbers, in this case 9 and 10. Can you see why?)

Anyway, hope folks here find it interesting too.

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[–] flubba86@lemmy.world 5 points 15 hours ago (1 children)

I've used many calipers with a vernier scale, but for some reason I've never seen the use of slots like this to simplify and highlight the reading. It's actually a very obvious thing now I've seen it. Are there any commercial calipers that have it?

[–] monotremata@lemmy.ca 3 points 7 hours ago

Not as far as I know. Practically speaking there are several disadvantages--the slots limit the light on the markings, parallax effects can mess with the reading, it requires two full surfaces sliding against each other which increases friction, etc. Plus with a regular vernier scale you can see both sides of a line, which could give you a better sense of how they line up ("vernier acuity"). But in a case like this, where precision isn't a top priority and ease of use might outrank it, I think there's an argument to be made for it.

[–] j4k3@lemmy.world 4 points 1 day ago (1 children)

Very cool. I was thinking about ways of making a potentiometer knob on an audio amp more visually interesting. The moire effect might be one to play around with.

I don't think I would trust this one in practice, but the effect is interesting. I found it far more necessary to learn the vernier scale with micrometers. It felt much more useful understanding the practical limitations and scope of when to use calipers versus a mic. While there are super accurate calipers, relatively cheap calipers and micrometers are far cheaper and easier for most people to access.

When it comes to radius gauges I trust these more than any of the others I have tried:

I know this kinda isn't the point, but using it as an excuse to share – the fishing leader line to hold a set like this is key to making them super handy. Unfortunately I have only used micrometers on a few 3d printing projects. Those are more used within the machining realm.

[–] monotremata@lemmy.ca 2 points 1 day ago

Yeah, it's definitely not the most precise thing. It's good to around ±1mm. I tried to measure 1.75mm filament with it, and it just reads 1, not even between 1 and 2, so for critical measurements the physical matches are definitely better.

And yeah, here the vernier effect is not giving very high precision; it's just giving a way to space the marks out enough to be printable, but indicate movements that are as small as a printed line.

[–] FeatherConstrictor@sh.itjust.works 3 points 2 days ago (1 children)

I find this useful even though I understand precisely nothing about what this is for how it's used and how it works. Thanks for the photos and write up though

[–] monotremata@lemmy.ca 2 points 1 day ago (1 children)

Sorry, just realized I also had the wrong link for the gallery that included photos of the tool in use! I edited the post, but here's the corrected version of that: https://imgur.com/gallery/moire-vernier-radius-gauge-design-3d-printing-ajy0GBg

[–] FeatherConstrictor@sh.itjust.works 2 points 22 hours ago (1 children)

Oh man that clears up so much thank you! Super cool tool, impressed by this :)

[–] monotremata@lemmy.ca 2 points 22 hours ago

I wouldn't have caught that the gallery link was wrong if you hadn't mentioned not knowing how the tool was used, so thank you as well!

[–] monotremata@lemmy.ca 3 points 2 days ago

Sorry all! I meant to post a video of the moire/vernier effect in action, which is the most eye-catching part of the whole project, as the main image for the post, but it didn't upload. And now when I try to edit in a link, or post a link to it in the comments, it's telling me "blocked URL." But there's a link on the printables page, and the version with the older version is in the imgur gallery which is linked.

[–] MxRemy@piefed.social 2 points 2 days ago (1 children)

From a big vernier caliper fan, this RULES!! 😍

[–] monotremata@lemmy.ca 2 points 1 day ago (1 children)

Vernier calipers are absolutely ingenious, and it's a shame that more people don't know how to use them.

[–] MxRemy@piefed.social 2 points 1 day ago

I definitely agree lol, that's why I teach people how in the local library makerspace. We've a really nice Mitutoyo accurate down to 0.02mm!